[build][mips] Make libatomic configs relative

NOTRY=true
TBR=sergiyb@chromium.org

Bug: v8:8291
Change-Id: I47445d10bd19beeacc90321e9177f0959b3b2f13
Reviewed-on: https://chromium-review.googlesource.com/c/1297316
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56934}

infra/mb/mb_config.pyl

@@ -662,10 +662,10 @@
     },
 
     'mips_bundled_toolchain': {
-      'gn_args': 'custom_toolchain="//tools/toolchain:mips-bundled" '
-                 'ldso_path="//tools/mips_toolchain/sysroot/usr/lib/ld.so.1" '
-                 'gcc_target_rpath="//tools/mips_toolchain/sysroot/usr/lib:'
-                 '//tools/mips_toolchain/mips-mti-linux-gnu/lib:\$ORIGIN/."',
+      'gn_args': 'custom_toolchain="tools/toolchain:mips-bundled" '
+                 'ldso_path="tools/mips_toolchain/sysroot/usr/lib/ld.so.1" '
+                 'gcc_target_rpath="tools/mips_toolchain/sysroot/usr/lib:'
+                 'tools/mips_toolchain/mips-mti-linux-gnu/lib:\$ORIGIN/."',
     },
 
     'msan': {